Family devices: shared-screen family board with a who-is-this profile picker

- Admin can make a screen a family device; it opens on a family board
- Name tiles with KID labels; kids tap, others enter a PIN (lockout after 5 wrong tries)
- Name label with Switch user, auto-return to the board after 5 idle minutes
- Short 30-minute sessions on family devices
- Settings section for PIN and turning a device on or off
- Test, README and roadmap updated

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

public/index.html

@@ -102,6 +102,7 @@
 <script src="/rows.js"></script>
 <script src="/keys.js"></script>
 <script src="/inbox-view.js"></script>
+<script src="/device-ui.js"></script>
 <script src="/boot.js"></script>
 <script src="/shell.js"></script>
 </body>